Document Number: 002-14786 Rev. *E

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CYW20704

2. Integrated Radio Transceiver

The CYW20704 has an integrated radio transceiver that has been optimized for use in 2.4 GHz Bluetooth wireless systems. It has

been designed to provide low-power, low-cost, robust communications for applications operating in the globally available 2.4 GHz

unlicensed ISM band. The CYW20704 is fully compliant with the Bluetooth Radio Specification and enhanced data rate (EDR) spec-

ification and meets or exceeds the requirements to provide the highest communication link quality of service.

2.1 Transmit

The CYW20704 features a fully integrated zero-IF transmitter. The baseband transmit data is GFSK-modulated in the modem block

and upconverted to the 2.4 GHz ISM band in the transmitter path. The transmitter path consists of signal filtering, I/Q upconversion,

output power amplifier, and RF filtering. The transmitter path also incorporates pi/4-DQPSK for 2 Mbps and 8-DPSK for 3 Mbps to

support EDR. The transmitter section is compatible to the Bluetooth Low Energy specification. The transmitter PA bias can also be

adjusted to provide Bluetooth class 1 or class 2 operation.

2.1.1 Digital Modulator

The digital modulator performs the data modulation and filtering required for the GFSK, pi/4 – DQPSK, and

8 – DPSK signal. The fully digital modulator minimizes any frequency drift or anomalies in the modulation characteristics of the trans-

mitted signal and is much more stable than direct VCO modulation schemes.

2.1.2 Digital Demodulator and Bit Synchronizer

The digital demodulator and bit synchronizer take the low-IF received signal and perform an optimal frequency tracking and bit-syn-

chronization algorithm.

2.1.3 Power Amplifier

The fully integrated PA supports Class 1 or Class 2 output using a highly linearized, temperature-compensated design. This provides

greater flexibility in front-end matching and filtering. Due to the linear nature of the PA combined with some integrated filtering, exter-

nal filtering is required to meet the Bluetooth and regulatory harmonic and spurious requirements. The transmitter features a sophis-

ticated on-chip transmit signal strength indicator (TSSI) block to keep the absolute output power variation within a tight range across

process, voltage, and temperature.

2.2 Receiver

The receiver path uses a low-IF scheme to downconvert the received signal for demodulation in the digital demodulator and bit syn-

chronizer. The receiver path provides a high degree of linearity, an extended dynamic range, and high-order on-chip channel filtering

to ensure reliable operation in the noisy 2.4 GHz ISM band. The front-end topology with built-in out-of-band attenuation enables the

CYW20704 to be used in most applications with minimal off-chip filtering. For integrated handset operation, in which the Bluetooth

function is integrated close to the cellular transmitter, external filtering is required to eliminate the desensitization of the receiver by

the cellular transmit signal.

2.2.1 Digital Demodulator and Bit Synchronizer

The digital demodulator and bit synchronizer take the low-IF received signal and perform an optimal frequency tracking and bit syn-

chronization algorithm.

2.2.2 Receiver Signal Strength Indicator

The radio portion of the CYW20704 provides a Receiver Signal Strength Indicator (RSSI) signal to the baseband, so that the control-

ler can take part in a Bluetooth power-controlled link by providing a metric of its own receiver signal strength to determine whether

the transmitter should increase or decrease its output power.

2.3 Local Oscillator Generation

Local Oscillator (LO) generation provides fast frequency hopping (1600 hops/second) across the 79 maximum available channels.

The LO generation subblock employs an architecture for high immunity to LO pulling during PA operation. The CYW20704 uses an

internal RF and IF loop filter.

2.4 Calibration

The CYW20704 radio transceiver features an automated calibration scheme that is fully self contained in the radio. No user interac-

tion is required during normal operation or during manufacturing to provide the optimal performance. Calibration optimizes the per-

formance of all the major blocks within the radio to within 2% of optimal conditions, including gain and phase characteristics of filters,

matching between key components, and key gain blocks. This takes into account process variation and temperature variation. Cali-

bration occurs transparently during normal operation during the settling time of the hops and calibrates for temperature variations as

the device cools and heats during normal operation in its environment.